165 / 2019-06-03 10:27:18

Control of the quality of tight sandstone reservoirs on the diagenetic system of the second member of Upper Triassic Xujiahe Formation (T3x2) in Zhongtaishan area, Sichuan Basin

Diagenetic system, Sichuan Basin, The second member of Xujiahe Formation, tight sandstone reservoir, reservoir quality

The differences in diagenetic systems have different control effects on reservoir quality. From the perspective of diagenetic system, this study analyzes the control of the quality of the tight sandstone reservoirs of the Upper Triassic Xujiahe Formation in Zhongtaishan area. Based on seismic data, cast thin section, cathodoluminescence, X-ray diffraction, SEM, inclusion analysis and porosity and permeability data, it can be found that the dissolution products of feldspar and carbonate lithoclasts are associated and they fill up the intergranular and intragranular dissolved pores, the dissolution products of Well ZT1 and Well WT1 do not show the characteristics long-distance migration; the palaeosalinity of Well ZT1 is lower than that of Well WT1. The early fractures of Well ZT1 were not filled in the early stage of diagenesis, and the late fractures were mostly filled-semi-filled with cements, but there was no fracture developed in Well WT1. The study found that the second member of Xujiahe Formation of Well ZT1 in the research area was an open diagenetic system in the early stage of diagenesis and gradually changed into a closed diagenetic system in the late stage; however, the second member of Xujiahe Formation of Well WT1 was always a closed diagenetic system during diagenesis. Through the quantitative calculation of the difference between the current dissolution porosity and contents of the clay cement and siliceous cement, the reservoir quality of Well WT1 and Well ZT1 generally declines, but there are some differences in the reservoir quality between the two. The second member of Xujiahe Formation of Well ZT1 is an open-closed diagenetic system, the outward migration of the dissolution products is limited and the reservoir quality slightly improves, therefore, the physical properties of Well ZT1 are negatively correlated with the total contents of siliceous and clay cements. The second member of Xujiahe Formation of Well WT1 was always a closed diagenetic system, the dissolution products exist in the pores of the reservoir as cements, the reservoir quality cannot improve, therefore, the physical properties of Well WT1 are positively correlated with the total contents of siliceous and clay cements. The study shows that high-quality tight sandstone reservoirs of the second member of Xujiahe Formation in Zhongtaishan area are essentially controlled by the evolution of diagenetic systems.The coupling of early open diagenetic systems and late closed diagenetic systems is the key to the formation of high-quality reservoirs. The opening and closing of fractures are important factors affecting diagenetic systems.